Position Sensitive Wall Current Monitor

Position sensitive WCM

The monitor is basically a WCM. A ceramic ring, diameter 100mm, length 40mm and wall thickness 5mm interrupts the image current as it flows along with the beam on the inside surface of the vacuum chamber. Distributed around the ring are 32 resistors, each consisting of three 10Ω resistors in series. A voltage develops across the resistors as the wall current passes through.

A shielding box, with two Philips 2E8 ferrite rings to get better LF response, surrounds all. At four equally spaced points around the ceramic ring, signals are picked off. Anzac H9 hybdrids (2MHz-2GHz) are used to combine the signals into horizontal an vertical differences and a sum signal.

The monitor is presently installed in SS00 of the PS.

Some PU properties
Bandwidth Σ:	2.7MHz-1.5GHz
Bandwidth Δ:	9.4MHz-1.5GHz
Rt :	1.26 Ω
Sx :	40mm
Sy :	40mm

References:

• G. Schneider, "A 1.5GHz wide-band beam position and intensity monitor for the electron-positron accumulator", CERN-PS 87-9 (1987), PAC'87, March 1987
• J. Belleman, "A note on frequency response equalization", wcm00.pdf, March 2010